Process controllers generally consist of a series of input ports, a control mechanism, and a series of output ports. Historically process controls were pneumatic devices where the inputs and outputs were pneumatic pressures, and the control element was a mechanical force balancing device. The operator tuned the device by turning a screw to position a lever, to tension a spring or to perform a similar mechanical adjustment.
Pneumatic devices are being replaced by simple electrical devices and more recently by devices that include small computers. The latter offer great accuracy, and are adaptable to a wide variety of applications. By electing among the various program features, the same device can be configured for use in many more situations, or be quickly reconfigured for different conditions in the same situation. Adding additional computational ability then extends the utility of the device at little per unit cost.
The addition of computing components to controllers is not without problems. As the list of configurable features become more extensive, the operator is required to knowledgeably select from the list of options. The lack of self-obviousness is then an emerging difficulty in configurable controllers. One awkward solution is for the operator to carry an instruction book with him.
Another difficulty is the mechanical communication between the operator and the controller. The controller has become a computer, requiring a list of data inputs to set its configuration. One solution has been to add a keyboard to the controller itself. The operator uses the general keyboard to enter values and to select options offered by the device. The number of keys on such keyboards can be quite extensive, verging on that of a typical computer terminal. An alternative solution is to provide a series of specialized keys for entering particular items. In either case, the area of the face of a controller in a device rack is limited which in turn limits the number of conveniently available keys. Some controllers overcome the area limitation by placing the keyboards on the side of the device. The controller is then slid partially out from the rack, exposing the keyboard for command entry. Another solution has been to place a door on the controller's faceplate behind which additional keys are positioned. Extensive keybords are expensive, take up space, and by themselves do not constitute a convenient solution to the on-site configuration problem.
A solution to the mounted keyboard, is to dismount the keyboard from the controller and place it in a hand-held unit. The operator carries the hand device from place to place and plugs it into a controller to enter device information. The hand-held device is not a fully satisfactory solution. One hand device may be required for each separate controller. The operator is then obligated to remember to carry the device, or devices and possibly an instruction book. Further, a hand-held keyboard of itself is not an adequate solution to the problem of setting up a complex device.
Another solution is to include in the controller a read and display sequence. A series of interaction points for data entry are linked as a chain. The operator presses a button to sequence the device to a point for interaction, reads or sets a value, and then cycles the device back to its beginning state. By returning to the initial entry at the end of the series, the straight chain of entry becomes a ring structure. A ring structure of interaction points allows the operator to make a series of entries and repeat the sequence reading and checking his entries. In an initial set up, usually all of the options must be set, in which case a single chain or ring type set up procedure is acceptable. The operator does not need to carry an instruction book, or a hand held device, yet a limited number of keys are conveniently present. No expensive or extensive keyboard is required. Only a few keys and a small display are present. However, the operator must repeatedly press one or more faceplate keys to position the device in the command loop.
Controllers are becoming complex, and the number of interaction points is increasing from the approximately just a few steps to a hundred, or more. One problem that occurs is the operator is inconvenienced by the numerous keystrokes required to position the device state in a long list of interaction points. Another problem is the operator may become confused as to what the current interaction point is; what is being entered or how to get to a different interaction point. The confusion is particularly likely where the category of information being entered changes.
Consequently, a need exists for improvements in the field of controller devices having selectable options so that with a limited number of input keys, a quick and self evident set up procedure may be accomplished.